1. Field of the Invention
The present invention relates to radio communication systems, and is more particularly related to a satellite packet switched communication system utilizing a medium access control (MAC) protocol to establish a channel for packet transfer.
2. Discussion of the Background
Modern satellite communication systems provide a pervasive and reliable infrastructure to distribute voice, data, and video signals for global exchange and broadcast of information. These satellite communication systems have emerged as a viable option to terrestrial communication systems for carrying Internet traffic as well as telephony traffic. Another popular application is direct television broadcasting, which has provided a competitive alternative to cable television systems. Irrespective of the application, a satellite communication system must be designed to support the largest possible traffic capacity, which can translate to lower cost per telephone circuit, or television service, for example, and thus, to increased revenue for the system operator. In addition, satellite communication systems are required to exhibit user response times that are comparable to competing terrestrial systems. That is, the hosts that connect to a user terminal (UT) demand that the delay of the satellite system be minimized, thereby reducing user response time.
To provide packet switched services, a satellite communication system must employ a robust and efficient protocol stack, particularly at the physical, data link, and networking layers (in terms of the OSI (Opens Systems Interconnection) model). One approach has been to utilize the medium access control (MAC) and Radio Link Control (RLC) layer of the ETSI (European Telecommunications Standards Institute) GSM (Global Satellite Mobile Communications) GPRS (General Packet Radio Service) standard (e.g., GSM 03.64) to establish communication between satellite terminals and gateway stations. This standard defines the procedures that enable multiple user terminals to share a common transmission medium by providing contention resolution in the event of collisions. GSM, however, is a global standard that is promulgated by the ETSI for digital cellular terrestrial communication, and thus, is not optimized for a satellite communication system.
Because the MAC/RLC layer of the GSM GPRS standard is primarily focused on a terrestrial system, this conventional protocol has a number of drawbacks. One major drawback is that the protocol requires a two-phase access scheme to establish a communication channel. In the GPRS protocol, the terminal must transmit a packet channel request message in a slotted aloha channel. This packet channel request message is limited in length, containing only 8 or 11 bits. This length restricts the amount of information that can be conveyed; therefore, all the necessary user terminal information, such as the terminal ID, the terminal type (given that different terminal types might have different physical channel requirements), the reason for the packet channel request, the required capacity or the quality of service requirements, and etc. cannot be properly captured in such a small message length. The network needs the user terminal information to perform an uplink resource assignment. Thus, in response to the terminal""s packet channel request message, the network transmits a packet uplink assignment message, assigning the terminal a single packet channel block simply to transmit the required information. This information is, subsequently, transmitted by the terminal to the network in the packet resource request message to which the network can finally respond to the terminal with the required resource assignment. The process of transmitting, first the packet channel request message in a slotted aloha channel, and second the packer resource request message in a single block assignment, is referred to as two stage access. This is the normal method of packet channel access by a terminal in GSM GPRS.
This two-phase access scheme is performed for every packet channel communication transmission. In a system with a one-way propagation delay of about 250 ms (which is typical of a satellite communication system), this approach introduces about 1 second of delay, excluding the processing delays before a packet resource can be assigned for the transmission of data. Such a scheme is acceptable in a system with short propagation delay; however, in a satellite communication system, this delay translates to significant increased user response times stemming from the protocol.
GSM GPRS protocol and other conventional protocols do not allow the UT or the network to transmit signalling control information and data within the same RLC block.
With respect to the Internet, the Transmission Control Protocol (TCP) and the Internet Protocol (IP) are the de facto standards and are used by all the major application layer protocols (e.g., FTP (File Transfer Protocol), HTTP (Hyper Text Transfer Protocol), and SMTP (Simple Mail Transfer Protocol).
In a system that provides a medium over which end-user applications use the TCP/IP, the inefficiencies of the two-phase access scheme is even more pronounced. Typically, data is segmented into numerous packets for transport over a TCP network. TCP is responsible for managing the reliable transmission of these data packets through the network; one of the mechanisms by which TCP accomplishes this task is through the issuance of acknowledgements for received packets. Therefore, the two-phase access procedure would be performed for each TCP acknowledgement. Over the course of a transaction, such as accessing a web site, the two-phase access scheme imposes a heavy cost on the network performance.
Based on the foregoing, there is a clear need for improved approaches for establishing a communication channel for packet transfer in a radio communication system. There is also a need to reduce user response time. There is also a further need to enhance network throughput. Therefore, an approach for streamlining the packet channel access procedure using a more efficient protocol is highly desirable.
The present invention addresses the above stated needs by providing a capability to enhance system throughput of a packet radio communication system
The present invention relates to the transmission of packets over a packet radio communication system. When a user terminal is in a synchronized state, the terminal utilizes a single-phase access procedure according to a medium access control (MAC) protocol and radio link control (RLC) protocol to obtain a packet data channel. The gateway station receives the packet channel request message and transmits an assignment message that specifies a channel assignment based upon the user terminal information. The present invention combines attributes of the packet channel request with the packet resource request messages. The user terminal has the capability to mix control and data packets. The system allocates unused uplink resources to the user terminals for appropriate use by the terminals, thereby saving valuable time and optimizing the use of radio resources to improve system responsiveness and throughput.
According to one aspect of the invention, a method is provided for establishing a packet communication channel in a radio communication system to exchange packets. The method includes receiving a packet channel request message that specifies user terminal information from a terminal over a contention channel according to a prescribed protocol. In addition, the method encompasses transmitting an assignment message that specifies a channel assignment based upon the user terminal information, wherein the packets are transmitted over a channel according to the channel assignment. Under this approach, response times are minimized.
According to another aspect of the invention, a radio communication system for exchanging packets comprises a terminal that is configured to transmit a packet channel request message that specifies user terminal information using a contention channel according to a prescribed protocol and a single access scheme. A gateway station is configured to receive the packet channel request message and to transmit an assignment message that specifies a channel assignment based upon the user terminal information to the terminal, wherein the terminal is configured to transmit the packets over a channel based on the channel assignment. The above arrangement advantageously provides enhanced system efficiency.
In another aspect of the invention, a computer-readable medium carrying one or more sequences of one or more instructions establishing a communication channel in a packet radio communication system to exchange packets is disclosed. The one or more sequences of one or more instructions include instructions which, when executed by one or more processors, cause the one or more processors to perform the step of receiving a packet channel request message that specifies user terminal information from a terminal over a contention channel according to a prescribed protocol. Another step includes transmitting an assignment message that specifies a channel assignment based upon the user terminal information. The packets are transmitted over a channel according to the channel assignment. This approach advantageously increases network throughput.
In yet another aspect of the invention, a satellite communication system for establishing a communication channel to exchange packets comprises means for receiving a packet channel request message that specifies user terminal information from a terminal over a contention channel according to a prescribed protocol. The system also includes means for transmitting an assignment message that specifies a channel assignment based upon the user terminal information. The packets are transmitted over a channel according to the channel assignment. Accordingly, the above approach advantageously reduces system delay.
In yet another aspect of the invention, a method for establishing a communication channel in a packet radio communication system to exchange packets is disclosed. The method includes determining whether a terminal is synchronized in time with the packet radio communication system. The method also includes selectively establishing a packet data channel using a single-phase access scheme based upon the determining step, and transmitting the packets by the terminal via the packet data channel over the packet radio communication system. This approach advantageously provides an efficient use of system resources.